public_api_example_deepseek.rs

If the `InternalAPI` should not be part of the `ItemsCollection`, we can decouple it by using **dependency injection** or **traits**. This way, the `ItemsCollection` can interact with the `InternalAPI` without directly owning or knowing about its implementation. This approach aligns with the **Dependency Inversion Principle** and makes the code more modular and testable.

Here’s how you can refactor the code to achieve this:

---

### Refactored Code

```rust
use reqwest::blocking::Client;
use serde::Serialize;
use std::collections::HashSet;

// Public API
pub struct ItemsCollection {
    items: HashSet<String>,
}

impl ItemsCollection {
    pub fn new() -> Self {
        Self {
            items: HashSet::new(),
        }
    }

    // Public method to add an item
    pub fn add_item(&mut self, item: String, internal_api: &impl InternalAPI) {
        self.items.insert(item.clone());
        internal_api.send_item_to_external_service(&item);
    }

    // Public method to remove an item
    pub fn remove_item(&mut self, item: &str, internal_api: &impl InternalAPI) -> bool {
        if self.items.remove(item) {
            internal_api.send_item_to_external_service(item);
            true
        } else {
            false
        }
    }
}

// Internal API Trait
pub trait InternalAPI {
    fn send_item_to_external_service(&self, item: &str);
}

// Concrete implementation of the InternalAPI trait
pub struct ExternalServiceAPI {
    client: Client,
    external_service_url: String,
}

impl ExternalServiceAPI {
    pub fn new() -> Self {
        Self {
            client: Client::new(),
            external_service_url: "https://example.com/api/items".to_string(),
        }
    }
}

impl InternalAPI for ExternalServiceAPI {
    fn send_item_to_external_service(&self, item: &str) {
        let item_details = ItemDetails {
            name: item.to_string(),
        };

        if let Err(e) = self.client.post(&self.external_service_url)
            .json(&item_details)
            .send() {
            eprintln!("Failed to send item to external service: {}", e);
        }
    }
}

// Struct representing the item details to be sent to the external service
#[derive(Serialize)]
struct ItemDetails {
    name: String,
}

fn main() {
    let mut collection = ItemsCollection::new();
    let internal_api = ExternalServiceAPI::new();

    // Adding items
    collection.add_item("item1".to_string(), &internal_api);
    collection.add_item("item2".to_string(), &internal_api);

    // Removing an item
    collection.remove_item("item1", &internal_api);
}
```

---

### Key Changes and Explanation

1. **Decoupling `InternalAPI` from `ItemsCollection`**:
   - The `ItemsCollection` no longer owns or directly depends on the `InternalAPI`.
   - Instead, the `InternalAPI` is passed as a parameter to the `add_item` and `remove_item` methods. This is **dependency injection**.

2. **Trait for `InternalAPI`**:
   - A trait `InternalAPI` is defined to abstract the behavior of sending item details to an external service.
   - This allows you to define multiple implementations of the `InternalAPI` (e.g., for testing, mocking, or different external services).

3. **Concrete Implementation**:
   - The `ExternalServiceAPI` struct implements the `InternalAPI` trait.
   - It contains the logic for sending HTTP POST requests to the external service.

4. **Flexibility and Testability**:
   - By using a trait, you can easily mock the `InternalAPI` for unit testing or swap out the implementation without modifying the `ItemsCollection`.

5. **Usage in `main`**:
   - The `ExternalServiceAPI` is instantiated and passed to the `ItemsCollection` methods when adding or removing items.

---

### Benefits of This Approach

- **Separation of Concerns**: The `ItemsCollection` is only responsible for managing the collection of items, while the `InternalAPI` handles communication with the external service.
- **Testability**: You can create a mock implementation of the `InternalAPI` trait for testing purposes.
- **Extensibility**: You can easily add new implementations of the `InternalAPI` trait without modifying the `ItemsCollection`.

---

### Example of a Mock Implementation for Testing

```rust
#[cfg(test)]
mod tests {
    use super::*;

    // Mock implementation of InternalAPI for testing
    struct MockInternalAPI {
        sent_items: Vec<String>,
    }

    impl MockInternalAPI {
        fn new() -> Self {
            Self { sent_items: Vec::new() }
        }
    }

    impl InternalAPI for MockInternalAPI {
        fn send_item_to_external_service(&self, item: &str) {
            // Simulate sending the item by storing it in a vector
            self.sent_items.push(item.to_string());
        }
    }

    #[test]
    fn test_add_item() {
        let mut collection = ItemsCollection::new();
        let mock_api = MockInternalAPI::new();

        collection.add_item("item1".to_string(), &mock_api);

        assert!(collection.items.contains("item1"));
        assert_eq!(mock_api.sent_items, vec!["item1"]);
    }
}
```

This mock implementation allows you to test the `ItemsCollection` without making actual HTTP requests.

---

This design ensures that the public API remains clean and consistent, while the internal API is decoupled and can be easily modified or replaced.